Despite its potential, the use of Raman spectroscopy for real-time quantitative reaction monitoring is still rather limited. The problems of fluorescence, laser instability, low intensities, and the inner filter effect often outscore the advantages as narrow bands, the use of glass fibers, and low scattering of water and glass. In this paper, we present real-time quantitative monitoring of the catalyzed Heck reaction by using the solvent as internal standard. In this way, all multiplicative distortions, e.g., laser intensity variations or absorbance of the laser light, can be corrected for. We also show that a limited amount of fluorescence does not hamper the analysis. Finally, we present a new method to correct for the inner filter effect, i.e., the absorbance of Raman scattered light by the reaction medium. Simultaneous absorption measurements of the reaction mixture enable accurate correction of Raman signals for the inner filter effect. Thus, for reaction monitoring applications, a Raman spectrometer should be equipped with an absorbance measurement device.

Rh-mediated polymerization of carbenes gives access to new highly substituted and stereoregular polymers. While this reaction is of interest for the synthesis of syndiotactic polymers that are functionalized at every carbon atom of the polymer backbone, the catalyst activation, chain-initiation, and chain-termination processes were so far poorly understood. In this publication we present new information about these processes on the basis of detailed end-group analyses, dilutionkinetic studies, and a comparison of the activity of well-defined catalysts containing a preformed Rh−C bond. All data point toward complex catalyst activation processes under the applied reaction conditions. The use of well-defined Rh I (cod)-alkyl, aryl, and allyl complexes does not lead to better initiation efficiencies or higher polymer yields. MALDI-ToF MS of the oligomeric fractions indicates that during the incubation time of the reaction, the precatalysts are first transformed into oligomer forming species with a suppressed tendency toward β-hydrogen elimination, and accordingly a shift to saturated oligomeric chains that are terminated by protonolysis. Further catalyst modifications lead to a shift from atactic oligomerization to stereoregular high molecular weight polymerization activity. Dilution-kinetic studies reveal that under diluted conditions two different active species operate that differ largely in their chain-termination behavior. Analysis of the reaction products by MALDI-ToF MS also allows conclusions about chain-initiation and chain-termination. Chain-initiation can occur by insertion of a preformed carbene into a Rh-ligand or Rh-hydride bond or by (internal or external) nucleophilic attack of water and/or alcohol on a Rh-carbene moiety. Chain-termination takes place mainly by (nucleophilic) protonolysis involving water or alcohols, while β-H elimination plays only a minor role and is only observed for the shorter oligomers. The detection of ethoxy and hydroxyl end-groups demonstrates the importance of trace amounts of water and ethanol toward chain-initiation. Alcohols further function as a chain-transfer agent, and increasing the alcohol concentration accelerates the chain-transfer process (which remains however relatively slow compared to chain-propagation). On the basis of the chemical properties of the alcohols, we propose a chain-transfer mechanism involving nucleophilic attack of the alcohol (nucleophilic, σ-bond metathesis type, protonolysis). This further allows us to draw some (careful) new conclusions about the oxidation state of the actual polymerization species.

Synthetic polymers and comprehensive two-dimensional liquid chromatography (LC × LC) are a synergistic combination. LC × LC provides unique insights in mutually dependent molecular distributions. Synthetic polymers offer clear demonstrations of the value of LC × LC.

In this paper, Fourier-transform near infrared (FT-NIR) spectroscopy is used to monitor the kinetics of complex catalytic reactions in liquid phase. Gas chromatography (GC) is used as a reference method. Spectroscopic measurements generate large amounts of data and the calibration is usually time-consuming and complex. To reduce the calibration effort the spectral data is analysed using the net analyte signal (NAS) approach. The reaction of interest is the Heck reaction of iodobenzene (PhI) and n-butyl acrylate (NBA) to give n-butyl cinnamate (NBC). This reaction is studied by means of FT-NIR and GC and the time-resolved reaction profiles obtained are compared. Results of the two techniques are consistent and the spectral results show an excellent reproducibility. It was observed that the reaction has an initiation period that decreases with the increase of temperature. With bulky monodentate palladium catalysts the presence of this initiation period has up to now gone unnoticed.